Abstract: The valve device adjustably controls air flow through a mechanical ventilation duct, blocks propagation of flames through the duct, and selectively exhausts smoke through the duct. An air extraction terminal sleeve communicates with the ventilation duct and is provided with an outwardly facing valve seat. A support is mounted in the sleeve inwardly of the valve seat and an elongated guide extends adjustably through the support. An obturator is mounted on the guide outwardly of the support for adjustably controlling the flow area into the terminal sleeve, and includes an outwardly convex dome member fixedly secured to the outer end of the guide, and an inwardly convex valve member having conforming seating engagement with the dome member and arranged to conformingly engage the valve seat to block flow into the terminal sleeve.